This invention relates to a solvent-free, cold-setting organosiloxane composition containing liquid organopolysiloxane as a major component, and uses thereof. More particularly, it relates to a solvent-free, cold-setting organosiloxane composition of one-pack type which can form, when in contact with moisture, a polymer having polysiloxane bonds as a main chain and having a good flexibility, incombustible or fire-retardant properties, heat-resistant properties, alkali-resistant properties and water-impermeable properties, and which can be used for forming a transparent film, a coating material, a binder, a structure, etc. and uses of the composition.
Solvents have so far been important for preparing coating compositions, generally accounting for 45 to 50% of such paint compositions. More than 50 kinds of solvents are illustrated as major solvents. In particular, organic solvents are important and indispensable for dissolving or dispersing film-forming materials to impart a proper fluidity, coating properties and film-forming properties. Thus, organic solvents have so far been inevitable for producing coating compositions.
However, organic solvents can be described as dangerous objects due to their high combustibility and capability to induce various troubles (e.g., anesthesia, troubles of the central nervous system and the autonomic nervous system, troubles of liver and kidney, and inflammation of skin or eye), thus requiring control and caution in handling.
The environment of the earth cannot afford the use of such combustible, dangerous organic solvents which induce human troubles in daily commodities. Thus it has been eagerly desired to develop solvent-free coating compositions. Although aqueous emulsion coating compositions and powder coating compositions have been developed as solvent-free coating compositions. These coating compositions have failed to have sufficient properties.
Organosiloxanes to be used as the major component of the compositions of the present invention are known as typical compounds of organo-silicon compounds and are represented by the structural formula of R.sub.3 SiO(R.sub.2 SiO).sub.n SiR.sub.3, (R.sub.2 SiO).sub.n, etc. As is shown by the structural formulae, organosiloxanes have a chemical structure wherein inorganic siloxane bonds of Si--O and organic groups (e.g., alkyl groups, phenyl groups, aryl groups, alkoxy groups, acyloxy groups, etc.) are bound to each other. Thus, organosiloxanes have both inorganic features of silanol bonds (Si--OH) and organic features of C--C bonds or C--O bonds.
On the other hand, atomic bond energy of a C--C bond is 84.9 kcal/mol and that of a C--O bond is 80.9 kcal/mol, whereas that of a Si--O bond is as large as 106 kcal/mol (about 25% larger than that of the organic bonds). Therefore, it can be seen that the siloxane bonds are more stable than the organic bonds against physical energy such as heat or light and chemical energy such as oxidation.
Further, organic resins are liable to undergo radical decomposition when irradiated with light rays of the ultraviolet ray region since they are sensitive to light rays of 300 to 350 nm in wave-length. On the other hand, methyl type silicone resins are known to absorb almost no light rays in the ultraviolet ray region, thus being suggestively inert against ultraviolet rays and strongly weatherable.
About 50% of the siloxane bonds are believed to be ionic bonds, and bond rotation is easier due to their longer atomic bond distance and lower electron density, and thus the bond angle can be changed by a comparatively small amount of energy. Accordingly, chains of siloxane bonds are more flexible than chains of C--C bonds, and are more resistant against heat or physical energy impact, thereby providing materials with a high flexibility.
As is described above, organosiloxanes having Si--O bonds are different in many points from organic compounds constituted by C--C bonds or C--O bonds. In particular, the organosiloxanes can be clearly differentiated from those organic compounds which are susceptible to oxidation or combustion.
Polymer siloxane compounds wherein organosiloxane units are cross-linked and polymerized to form a main chain composed of Si--O bonds are called silicones or silicone resins and are popularly used. Of these silicones, organopolysiloxanes having two different functional groups per molecule are generally called by the name of silane coupling agents and have been widely investigated and used as modifying agents for inorganic or organic materials and additives. In addition, the silicone resins are being widely used as electronic and electric products and daily commodities.
The reaction mechanism of polymerization of organosiloxane to form a cured product is considered a condensation reaction or addition reaction of reactive siloxane in the presence of water. With the organosiloxane of the present invention, too, functional alkoxy groups react with water at ordinary temperature to cause a dealcoholation reaction and produce silanol groups (first step). Then, the silanol groups in turn react with the alkoxy groups of a cross-linking agent in the presence of a metal-containing catalyst to undergo a condensation reaction (e.g., dealcoholation, deoximation, removal of acetic acid, etc.), resulting in polymerization and formation of a polymeric cured product having a three dimensional network structure (second step).
In general, varnishes, coating compositions, adhesives, and the like are mainly based on organic resins. Recent living environmental regulations have required incombustible or fire retardant, pollution-free materials in many fields. Under such situations the use of organic solvents which are dangerous and can cause environmental pollution has been brought into question. Hence, pollution free materials involving no such problems have eagerly been desired.
In film forming coating compositions or coating materials, materials requiring a heating step to cure are limited as to scope of their application. Therefore, materials which can form a film at ordinary temperature are preferable from the standpoint of general-purpose properties. Conventional techniques of a film forming at ordinary temperature have employed the evaporation solvent or the addition a curing catalyst. In the case of adding a curing catalyst, it must be added immediately before application in view of shelf life of the material and, therefore, the material must be of two-pack type. The two-pack type materials have the defects that the two packs must be mixed immediately before application, and that their storage, work control and application procedures must be complicated.
One-pack type coating compositions utilizing curing with moisture are retained in a container capable of excluding the contents from contact with moisture, such as a tube or a cartridge for ensuring enough shelf life and, upon use, the contents of the container are exposed to the air. Thus, there have been required, coating compositions or like materials having sufficient shelf life which are of one-pack type and permit application at ordinary temperature.
In order to meet the requirement, siloxane compounds which have Si--O bonds resistant against heat or light and which have good weatherability, high heat resistance and good flexibility as has been described hereinabove have widely been investigated, part of the investigation results having been put into practice. Typical examples of the results and remaining problems are described hereinafter mainly referring to coating compositions and coating materials.
As a popular example of applying organsiloxanes to coating compositions, there are illustrated zinc-rich coating compositions developed in World War II. These coating composition comprise a hydrolyzed product of tetraethoxysilane diluted with about the same amount of isopropyl alcohol and about two-fold amount of zinc powder. This type of compositions is being widely used as anti-corrosive paints capable of forming a coating film at ordinary temperature.
There have been developed coating compositions prepared by diluting, with an organic solvent, polymers of organosiloxane or modified organosiloxane or copolymers thereof with various organic compounds, together with or without other organic resins. Most of the conventionally developed techniques are based on the above-described compositions. For example, a technique of preparing a modified tetraalkoxysilane as a filming agent in the presence of the same or more amount of a solvent, and applying the composition to an object, followed by air-drying or hot-air drying to form a heat-resistnt, anti-corrosive coat is disclosed in, for example, Japanese Examined Patent Publication No. S-63-28942.
There have been many examples of merely combining organic compounds (organic resins) and organosiloxanes to prepare coating materials or the like. Most of them require heating upon film formation. Typical example thereof is described in Japanese Examined Patent Publication No.S-55-41274, etc. wherein tetraethoxysilane and methyltriethoxysilane are mixed with polyvinyl butyral butylated methylolmelamine, and an object coated by the mixture is heated to 130.degree. C. to form a coating.
Many studies have been made on utilization of organosiloxane as a filming agent for a heat-resistant coating. Japanese Examined Patent Publication No.S-63-35183 discloses one typical example thereof wherein a coating composition prepared by adding a slight amount of an aluminum chelate compound to 50-80% by weight of a heat-resistant inorganic material (e.g., aluminum phosphate, zinc molybdate, calcium carbonate, zinc silicate powder, etc.), and adding thereto 20 to 50% by weight of a modified silicone resin is applied to an object, followed by baking at 180.degree. C. to form a heat-resistant coating.
In addition, many techniques of preparing a coating composition using an organosiloxane in an organic solvent and filming the composition at ordinary temperature or elevated temperature have been disclosed, one example being disclosed in Japanese Examined Patent Publication No.H-63-58191.
As an example of utilizing a pure organosiloxane, there is illustrated a technique of preparing a durable, stainproof transparent film composed of organosiloxane, an organotin compound and a volatile dimethylpolysiloxane (Japanese Unexamined Patent Publication No.H-3-68676).
A technique of using a keto-enol tautomer compound for stabilizing a curing catalyst of a metal-containing organic compound in the polymer-forming organosiloxane has also been disclosed. For example, Japanese Examined Patent Application No. S-48-17859 discloses this technique with respect to a mixed system of a linear copolymer having carboxyl groups within the molecule, an aluminum alcoholate complex compound, and a solvent. As a similar technique, Japanese Unexamined Patent Application No. H-1-129066 discloses to use a keto-enol tautomer compound together with a curing agent of chelate compound in a mixed system of a resin having isocyanato groups, hydroxyl groups, epoxy groups, carboxyl groups and/or amino groups partly reacted with alkoxysilane group or hydroxysilane group, an epoxy resin and an organic solvent.
On the other hand, alkali silicates having silanol groups such as water glass are known as inorganic compounds having Si--O siloxane bonds. Many investigations have been made on water glass since it is inexpensive and can form a polymer having siloxane bonds when applied at ordinary temperature. Many application studies have also been made to produce acid- and heat-resistant coating materials and solidified products from the inorganic silanol compounds including water glass.
However, polymers having siloxane bonds formed by curing the alkali silicate involve many problems due to copresence of an alkali component in the polymer. Further, inorganic polymers are generally hard and non-flexible, and it is essentially impossible to expect flexibility of a cured product formed of the inorganic polymer.
Water glass contains water, and hence it is of a so-called hydraulic type. Therefore, cured products of water glass from which water has been removed contain many pores. The pores inevitably impart susceptibility to water and water permeability to the cured products. Therefore, it is impossible to protect iron- or concrete-made substrates from corrosion by forming a protective coating of the hydraulic inorganic polymer. No materials of this type have attained the protecting ability.
Further, Si--O bonds are so reactive with alkali metal ions, regardless of whether the bonds are formed by an inorganic material or an organic material, that the bonds are easily cleaved, in the presence of an alkali metal ion such as sodium ion to form alkali silicate compounds. Therefore, compounds having Si--O bonds tend to have a poor alkali resistance even in a highly polymerized state, and application of such compounds having siloxane bonds to an alkaline material such as portland cement or concrete or to a situation which requires sea-water resistance or alkali resistance is quite limited.
In addition, the above-described inorganic coating materials or coating agents have a poor compatibility with organic materials and have generally no adhesion property to organic materials. Therefore, maintenance of objects having an organic coating using a general-purpose inorganic coating must be conducted after completely removing the existing organic coating. That is, it is impossible to apply the inorganic coating composition to an organic coating formed as a prime coat.
As has been seen with the above-described prior art, the application of the organopolysiloxane as a coating component has mostly begun with auxiliary addition to an organic compound-based coating composition containing an organic polymer or an organic resin having a main chain of C--C bonds and being excellent in filming properties, dilution properties with a solvent and drying properties after being coated for the purpose of improving the coating composition.
Hence, these conventional coating compositions inevitably contain the dangerous, trouble-causing organic solvents, and there have been seen no positive attempts to produce solvent-free coating compositions mainly using organosiloxane having incombustible or fire retardant Si--O bonds.
Namely, there have been completed no techniques of producing a coating composition in which the main chain is composed of only polysiloxane bond, [(.tbd.Si--O--).sub.n ], and the content of a silicon component is as high as 50% by weight or more in order to make the polymer incombustible or fire retardant (Condition 1), in which the metal components of silicon, titanium, zirconium, boron and aluminum are stably contained in a high concentration of 40% by weight or more in terms of MO.sub.y/2 (condition 2), which can be provided as a one-pack composition (Condition 3), and which can be cured at ordinary temperature according to a moisture-curing method to form an effective coating (Condition 4).
In addition, there have been completed no techniques of producing a coating composition which provides a coating having a siloxane bond polymer formed in the absence of a solvent and yet having sufficient flexibility, heat resistance, alkali resistance and water impermeability.
There have been no attempts of developing an inorganic coating composition having high performance by combining an organopolysiloxane with a liquid organometallic compound, particularly liquid alkoxyborate.
Additionally, concentrations or contents of metal element components of aluminum, boron, silicon, titanium and zirconium are presented by % by weight in terms of oxides and are in some cases abbreviated as "MO.sub.y/2 % by weight" in this specification.
In the above-described prior art, the existence of water or silanol groups in the solvent-free liquid organosiloxane composition allows curing reactions such as gelation and solidification to proceed during storage. There has not been disclosed a definite process of subjecting an organosiloxane-containing coating composition to a preliminary step of keeping the temperature at 100.degree. C. or less for a predetermined period of time in the absence of water to previously remove water or silanol groups carried by the organosiloxane or fillers added to the composition for ensuring one-pack stability and enough shelf life of the composition.
Particularly, there have been disclosed no techniques of subjecting a colored coating composition containing a pigment, a colorant or like filler to a special preliminary step for previously removing water or the like carried by the fillers to thereby avoid the curing reaction caused by water in the course of production or storage of the composition.
The inventors have given attention to the following fundamental problems which conventional transparent films, coating compositions, coating materials, binders, structures, etc. utilizing the above-described prior art polymers.
1) In the case of using an organic compound having C--C bonds as the main chain: PA0 2) In the case of using a silicon compound having incombustible Si--O bonds as the main chain: PA0 (1) A liquid composition constituted by a particular liquid organopolysiloxane and a cross-linking agent of organometallic compound can form a coating composition without any solvent; PA0 (2) Preliminary treatment of removing water and silanol groups contained in the composition permits storage of the composition in the one-pack form even in the presence of a curing catalyst; PA0 (3) When a metal-containing organic compound is allowed to be present in the particular organosiloxane liquid composition, it can form a cured polymer product when brought into contact with moisture in the atmosphere at ordinary temperature; and PA0 (4) The polymer having a main chain comprised of Si--O bonds including B--O bonds, Ti--O bonds, Zr--O bonds, etc. can exhibit highly functional polymer performance that cannot be obtained by the prior art.
(a) use of an organic solvent which is dangerous and harmful is inevitable; PA1 (b) the composition is quite susceptible to oxidation by heat or fire; PA1 (c) a poisonous and harmful gas is produced upon combustion; PA1 (d) the composition provides quite poor weatherability. PA1 (a) the composition provides poor flexibility; PA1 (b) the composition provides poor alkali resistance due to its high reactivity with an alkali metal element; PA1 (c) cured products containing Si--O bonds formed due to hydraulic property contain many pores, thus the products lack water impermeability; PA1 (d) the composition cannot be applied to a material composed of inorganic Si--O bonds since organic materials have no adhesion property to the inorganic surface. PA1 Transparent film: Transparent film such as clear coating material and protective material; PA1 Coating material: Paint, varnish, undercoating material and protective coating material having a certain thickness; PA1 Binder: Adhesive, binder, sealer, fixing agent for various aggregates, cementing material and anchoring agent; PA1 Structure: Building material, flooring and wall material, reinforcing material for a structural component, such as mass material, plate like material, network material, fibrous material and a fabric material, and structural shape formed by unifying aggregate or molding.
In addition to the above-described problems with the prior art, the inventors have given attention to the following facts. That is, in the conventional techniques of using siloxane bond-containing polymers, (1) energy- and labor-saving techniques enabling a one-pack form and application at ordinary temperature have not been completed, though the technique of applying a coating composition and heating it has been completed; (2) materials such as coating materials and coating compositions which permit in-situ application to form a coating with a incombustibility and fire retardance and with beautiful luster have not been widely used; (3) inorganic coating films which, when combusted, do not produce any poisonous and harmful gas have not been completed; and (4) a solvent-free, organosiloxane-containing coating composition has not been completed. With the above-described situation in mind, the inventors have acutely felt a deficiency of energy- and labor-saving techniques which, at the same time, can maintain the earth environment and have given attention thereto.